Reaction propulsion method



1958 D. R. CARMODY ET AL 2,357,736

REACTION PROPULSION METHOD Filed July 12, 1952 6/35 1 INVENTORS.

I Dan E. Garmody By Alex Z/efz ATT R/VE United States Patent REACTION PROPULSION METHOD Don R. Carmody, Crete, and Alex Zletz, Park Forest, 11]., assignors to Standard Oil Company, Chicago, 111., a corporation of Indiana This invention relates to reaction propulsion. More particularly, it relates to liquid fuels for use in a bipropellant rocket system. .Still more particularly, the invention relates to a method of rocket propulsion by the use of a nitric acid oxidizer and a hypergolic fuel, which'materials react to generate gases at high pressure and high temperature.

Reaction propulsion is now being used for many purposes. For uses in military missiles it is preferred to use a fuel system which is not dependent on atmospheric oxygen, i. e., rocket propulsion. At the present time rockets are used to assist the take-off of airplanes; this use is commonly known as IATO or ATO.

The fuels used for this purpose may be liquid or solid. The liquid fuels are divided into the monopropellants and the bipropellants. The monopropellants decompose to give hot materials which provide the driving force for the rocket; a well-known monopropellant is nitromethane. The bipropellant fuels consist of a fuel proper and an oxidizer. V l v In the bipropellant system the fuel and the oxidizer are injected separately and simultaneously into the combustion chamber of the rocket motor. may be supplied. to initiate the combustion or thecombustion may be spontaneous. The products of decomposition resulting from the reaction of the fuel and the oxidizer are discharged through an orifice-provided at the exit end of the combustion chamber to produce the.

driving force. p

Because of the possibilities of electrical and/or mechanical failure of the auxiliary methods of ignition such as spark or hot surface, it'is preferred .to use a propellant system which is self-igniting. A liquid fuel'which is self-igniting, i. e., spontaneously combustible when contacted with an oxidizer, is known as a hype Olic fuel.

Temperature has a very important effect on the activity of hypergolic fuels. Many materials which are hypergolic at temperatures of about +70" F. lose thischaractenistic when the temperature is lowered. The. temperature at the earths surface may vary from a high of about +120 F. to a low'of as much,as -65- F. The temperatures encountered at high altitudes are oftenas low as 65 F. and frequently are as. low as 510011. For military purposes the rocket-driven'missile mustoperate satisfactorily over the range-of about +120 -F..to "about '65 F. and preferably lower'than 65 -F.

An object of this invention -is a method ofjreaction proother object is a method of rocket propulsion, which" method is not dependent on'auxiliaryignition means forintiating combustion at temperatures'on the'order of 65 I x-The above-objects and other objects, which will -be- Ignition means specification and in the claims is intended to include all.

pulsion .by the interaction of a hypergolic fuel and a a nitric acid oxidizen'! Another object isjreaction propul- Patented Oct. 28, 1958 achieved by the interaction of a nitric acid oxidizer which contains not more than about 10 weight percent of nonacidic materials and a fuel consisting essentially of at least one member selected from the class consisting of:

A. Monoaliphatic phosphines which contain not more than 16 carbon atoms B. Dialiphatic phosphines which contain not more than 20 carbon atoms and wherein each aliphatic substituent contains not more than 16 carbon atoms.

C. Trialiphatic phosphines which contain not more than 9 carbon atoms and wherein each aliphatic substituent contains not more than 6 carbon atoms.

Further, the above defined fuel can be blended with not more than about one volume of an essentially nonhypergolic hydrocarbon to produce a mixed fuel that is hypergolic with nitric acid oxidizer Which contains not golic fuel, decreases as the non-acidic material contentof the acid increases. As the non-acidic material content increases the time for the reaction to begin becomes excessively long. (This time between the mixing andthe start of the combustion is known as the ignition delay.)

The term non-acidic material isintended to include substances that do not add to the energy content of the system, i. e., are not fuels and are used solely for the purpose of lowering the freezing point of the oxidizer. Water is the most commonly used freezing point depressant for nitric acid. By the addition of 10% of water it is possible to depress the freezingqpoint of nitric acid from -44 F. to -81 F. However, lower freezing points are obtainable by adding to the acid an aqueous solution of potassium nitrate or sodium nitrate. A mixture consisting of 92% acid, 4% water, and 4% potas-- sium nitrate has a freezing point of about 90 F. It has been found that when using the defined aliphatic phosphines of this invention that low temperature hypergolic activity is not obtainable when the nitric acid oxidizer contains more than about 10 weight percent of non-acidic materials.

Particularly suitable oxidizers are white fuming nitric acid (WF'NA) which, in the commercial grade, normally contains between about 2 and 3% of Water, and red fuming nitric acid =(RFNA) which, in the commercial grade, normally contains between about 3 and 5% of water and between about 5 and 22 weight percent of N 0. iNitrogen tetroxide 'N O is a satisfactory oxidizen for use above its freezing point. A mixture of N 0 andnitrous oxide, as described in U. S. 2,403,932, is a satisfactory oxidizer for use attemperatures as low as 60F. The term nitric acid oxidizer as used in this of the compositions described above which contain not more than 10% of non-acidic materials such as water and inorganic purposes.

It has been discovered that certain organic phosphines. have hypergolic properties with nitric acid oxidizers.

a'ttemperatures between about +l20 F. andabout -65 F. and insome cases at even lower temperatures One or more' of" the hydrogen atoms of phosphine PH may be replaced by one or more organic radicome, apparent in .the. detailed ;description,-have .been

cals. In this specification the words substituent andradical are used interchangeably.

Certain monoaliphatic phosphines, dialiphatic phosphines, trialiphaticphosphines and mixtures thereof are" :useful for theipurposes of this invention.

The term salts used for freezing point depressant through a ring carbon atom or through a side chain car-" bon atom. It has been found that the highly branched aliphatic substituents have desirably lower freezing points than the straight chain or slightly branched substit'uents. It is preferred to use branched aliphatic substituents. The presence of unsaturated linkages in the aliphatic'substituent improves the hypergolic activity so that a particularly useful aliphatic phosphine contains not only a highly branched aliphatic radical, but also contains one or more unsaturated linkages.

It has been found that the hypergolic activity of the various aliphatic phosphines is dependent upon the number of aliphatic substituents, upon the total number of carbon atoms contained in the aliphatic phosphine, and upon. the number of carbon atoms contained in each of the aliphatic substituents. In order to obtain a fuel which is usable at temperatures as low as 65 F., it is necessary that the monoaliphatic phosphines contain not more than16 carbon atoms. It has been found that the phos phines which contain two aliphatic substituents, i. e., dialiphatic phosphines, must contain not more than 20 car bon atoms in the molecule and furthermore, each-ali phatic substituent must not contain more than 16 carbon atoms. Thus a dialiphatic phosphine which contains a 16 carbon atom side chain must not contain more than 4 carbon atoms in the second side chain. It has been found that the completely substituted phosphines, i. e., trialiphatic phosphines, must not contain more than 9 carbon atoms in the molecule and furthermore, no aliphatic substituent must contain more than 6 carbon atoms. Thus a trialiphatic phosphine which contains a 6 carbon atom side chain will contain only a methyl and ethyl substituent as the other aliphatic substituents.

When it is desired to initiate the combustion at low temperatures on the order of 65 F. and simultaneously to have a very short ignition delay, it is' preferred to use the following fuels: monoaliphatic phosphines which contain not more than 12 carbon atoms; and dialiphatic phosphines which contain not more than 20 carbon atoms and wherein each aliphatic substituent contains not more than 12 carbon atoms.

The aliphatic phosphines are in general clear, mobile, high-boiling liquids with an unpleasant odor. They are fairly stable when exposed to elevated temperatures in the absence of air, but are extremely susceptible to oxidation by air even at ambient temperatures. Thus they are quite stable when stored in sealed containers such ass'toppe'red flasks and stainless steel drums. H

Several methods are known for the preparation of the aliphatic phosphines, e. g., the method of W; C. Davies. and W. J. Jones as described in J. Chem. Soc. (London),

p. 33 (1929); also, that of W. C. Davies in J. Chem. Soc. (London), p. 1043 (1933). Both of these methods in volve the Grignard reaction. to use the method described in U. 8.. Patent 2,584,112 which involves the reaction of phosphine and an olefin.

The products from all of these methods of preparation contain minor amounts of impurities. have a favorable effect on the freezing point of the aliphatic phosphines and appear to have no substantial adverse effect on hypergolic activity. It has also been foundthat the aliphatic phosphines which have been oxidized to a minor extent, e. g., 4 or are useful as hypergolic fuels. It is intended to include within: the. scope of the invention the use of aliphatic phosphines which contain.

minor amounts of impurities resulting-from the preparation thereof and also those which contain minor amounts of} oxidation products resulting from the oxidation of th al ph t c. ph phine- Th alip icphosphines are; particularly :suitable 'fn'els.

These impurities for rocket propulsion because of their low freezing points,

ing points they also have a considerable tendency to super-- cool, i. e., remain liquid at temperatures below the true freezing point. Most of these compounds do not form a crystalline mass when solid,but solidify in the form of a glass.

It has been found that hydrocarbons which are essentially non-hypergolic even at temperatures of about +120" F. can be blended with the defined aliphatic phosphines to produce a mixed fuel that is hypergolic with the defined nitric acidoxidizers. The other component blended with the aliphatic phosphine. to form the mixed fuel should have a low freezing point, on the order of 70 F., in order to obtain a mixed fuel that is operable at low temperatures. When an essentially non-hypergolic hydrocarbon is used as the other component of the mixed fuel, the boiling point of said hydrocarbon has an effect p the hydrocarbon is essentially non-reactive, A superior onthe hypergolic activity of the mixed fuel; it is preferred that the maximum boiling point of said hydrocarbon be below about 600 F. a a I Certain hydrocarbons, such as, shale oil fractions, olefins, some aromatic hydrocarbons, etc. are quite reactive with nitric acid oxidizers. When using these reactive hydrocarbonslessaliphatic phosphine is needed in the blend to produce a hypergolic mixed fuel than is needed when mixedfuel can be. made by blending a hypergolic fuel with one of the defined aliphatic phosphines. Examples of suitable hydrocarbons which are essentially non-hypergo'lic are virgin naphtha, kerosene; heater oil, Jet fuel,

. such as J-P-'-3 fuel, benzene, toluene, xylene, etc. It has been found that the composition of the aliphatic phosphine-hydrocarbon blend is substantiallyindependent of the number of aliphatic substituents present inthe ali-' phatic phosphine, It is noteworthy that these mixed fuels can be used with N 0 almost as effectively as with the undiluted aliphatic phosphine. This is unexpected since in general dilution has a very adverse eifect on the hypergol'ic activity with N 0 Ithas been found that when using an essentially V non-hypergolic hydrocarbon boiling below about 600 F.

that mixed fuels that are useful for the purposes of the invention can be made by blending about one volume of the defined aliphatic phosphine with aboutone volume of the essentially non-hypergolic hydrocarbon. The

, maximum dilution of the aliphatic phosphine will vary somewhat with the type of aliphatic phosphine and also with the type of hydrocarbon. When it is desired to.

have a mixed fuel that will have a short ignition delay at temperatures on' the order of '65' F., the mixed fuel" should contain not more than about 35 volume per- However, it is preferred a cent of the essentially non-hypergolic hydrocarbon and the aliphatic phosphines should be selected from at least.

one member of the class consisting of (1) mono'a'liphatic phosphine which contains not more. than 12 carbon atoms and (2') dialiphati'c'phosphines which contain not more" than 20 ca rbonatoms' and wherein each aliphatic subs'tituent contains. not more than 12 carbon atoms. A'

particularly suitable essentially non-hypergolic hydrocarbon consists; ofthe so-called JP-fuels which boil between about 325 and 550 F.

se erar aliphatic phosphines were prepared by the methods of the literature. The method or Davies and Jone supra was used to preparefa high purity tri-n-butyl phosphine. The method of Davies supra: was used to prepare a highpurity tri-secondary butyl phosphine, and also trimethyl phosphine. Thef'rnethod, of U. S. Patent 2,584,112; wasused to'react n-octene and Z-ethyl-l-hexene with phosphine;- In; each case a mixture of, substituted phosphines resulted and this mixture was carefully fractionated. to: produce. cuts which were predominantly mono, di; and: trialkyli phosphines; The physical: characteristics of the materials which were used in the test to be. described later are listed below:

Specific B. P. Phosphine Gravity F. F..-

F, mm H 1. 104-l07 750 120 0. 82 295-307 50 0. 8 260-410 90 0. 83 347-352 750 100 M0110 (n-octyl) 0. 82 207-248 50 +14 Mono (dodecyl) 0. 82 140-150 0. 2 100 1 Propylene tetrainer.

1 Very viscous fluid. v

The following tests illustrate the hypergolic activity of the above listed aliphatic phosphines. Hypergolic fuels known to the art are also listed for purposes of comparison. Y

Test 1 In this test the ignition characteristics of the oxidizer compositions were studied using a drop test method. This method utilizes a test tube, 1 in. x 4 in., containing 1 ml. of oxidizer. The fuel is added dropwise into the test tube by means of a syringe calibrated in 0.01 ml. markings. Usually 0.1 ml. of fuel is added per test; however, the fuel usage may vary between 0.01 and 0.2 ml. per ml. of oxidizer. Low temperature tests were carried out by cooling the -test tube and the oxidizer contained therein to the desired temperature by means of a Dry Ice-chloroform bath; a drying tube inserted into the top of the test tube excluded moisture. The fuel was cooled separately to the desired temperature. By supercooling, it was possible to carry out tests at temperatures below the freezing point of the fuel and of .the oxidizer. The time elapsing between the addition of the fuel to the oxidizer and ignition thereofthe ignition delay-was determined visually as either: very short, short, ignition or negative. A very short ignition delay corresponds to substantially instantaneous ignition.

Four difierent nitric acid oxidizers wereused in this I test. Theoxidizers were: commercial WFNA containing 2.6% water; commercial RFNAeontaining 3% water and 22% ofN O aqueous HNO containing 10% water and technical grade nitrogen tetroxide.

v (a). In this group ofruns the temperature of delays were noted for the various oxidizers.

(b) In this group ofruns the temperature was held at Phosphine BFNA 90% HNOa Di(2ethylhexyl) Short Short. ,Mono(2'ethyl.hexyl) do Ignition. Mono(nocty1) d Do. Mono(dodecyl) Do. Furiuryl alcohol Do. Aniline Fuel frozen.

Test 2 In order to measure more accurately the amount of fuel added and also to approach more closely a reproducible degree of mixing, a capillary tube test was also bothoxidizer and fuel was held at +7-5- F. and the ignition WFNA '(see Test -1) as the oxidizer.

used; A capillary tube of 2 mm. diameter or'less, with a syringe attached at one end, is filled with a measured amount of fuel undergoing the test; an air space is left at the end of the tube. The capillary tube is inserted into the oxidizer in a beaker and the fuel is injected into the acid by depressing the syringe plunger. By this capillary tube method, amounts of fuel on the order of 0.0002 ml. can be added to the oxidizer.

. The. runs in this group were carried out with the oxidizer and the fuel at +75 F. to determine the minimum volume of fuel required for ignition with 100 ml. of

' Minimum volume Phosphine: ml.

' Di(2-ethylhexyl) 0.0003 Mono(2-ethylhexyl) 0.0002 Mono(n-octyl) 0.0002 Mono(dodecyl) 0.0003

Furfuryl alcohol 0.006 Aniline 0.025

Test

Ignition Delay, Milliseconds Phosphine Tri-n-butyl Neg Neg. Di(Z-ethylhexyl) 0 Mono (2-ethylhexyl) 8 Mono(n-octyl) Mono (dode cyl) Test 4 In thistest the composition of a mixture of aliphatic phosphine and n-heptane which would be hypergolic at +75 F. was determined. The runs were carried out using WFNA and N 0 as. the oxidizers. The data below show the volume percent of n-heptane which can be tolerated in a hypergolic mixed fuel.

v Maximum Volume Percent n-Hept'ane Ihosphine WFNA N204 Trimethyl 40 (Approx) Di(Z BfilYlhGXYl) 40 v 40 Mono (Z-ethylhexyl) 40 40 Mono (n-octyl) r 50 50 Mono (dodecyl) 50 The above tests show clearly the extreme effectiveness of the defined alkylphosphines as hypergolic fuels with nitric acid oxidizers either alone or in admixture with essentially non-hypergolic hydrocarbon.

The annexed drawing illustrates schematically the motor and the fuel system ofa bipropellant rocket which can usefully utilize the fuels described herein. Referring to the drawing, vessel 11 contains a quantity of inert gas under high pressure; nitrogen or helium is a suitable gas. The gas is passed through line 12, through regulatory valve 13 which passes the gas into line 14 at a constant pressure. From line 14, the gas is passed into line 16 which is connected to the vessels containing the the'pressure of the gas from line 16Tforee s e oxidizer hrsug e .8 th o h s l qid" ys t i thfiittii gf al 19 hro n 21, n th tsh i i t 2 i combustion chamber 23. Combustion chamber 23 is provided with an exit orifice 24. Vessel 26 contains the main supply of fuel. The gas pressure forces the fuel out of vessel 26 through line 27, throngh solenoid actuated valve 28, and through line 29 to vessel 31. Vessel 31 may be used to contain a special starter fuel or an additional amount of the main fuel The pressure in line 2? forces the contents of vessel 31 through line 32, through solenoid actuated throttling valve 33, through line and through injector 36 into combustion ehambet 23,. The injectors 22 and 36 are so arranged the stream of liquid violently impinge and thoroughly intermingl e. The reaction of the fuel and the oxidizer results in the generation of a large volume of very hot gases which pass out of the combustionv chamber through orifice 24; the reaction from this expulsion'of gases drives the rocket.

For ordinary velocity flight a single fuel is used. In this illustration the fuel is a mixture of a monoalk-yl phosphine such as monododecyl phosphine and IP.3 fuel wherein the volume ratio of the two components is 1. In this method of operation both vessels '26 and 31 will contain this fuel. The oxidizer consists of a commercial red fuming nitric acid. The ratio, on a weight basis, between the oxidizer mixture and the fuel may be between about 1.5 and 5.0. In this example 3 lbs. of oxidizer composition are used per. pound of fuel. The missile is launched by activating the solenoids on valves 19 and 33. The oxidizer and the fuel are forced into the combustion chamber by the pressure of The walls of the combustion chamber become very.

hot from the heat of the burning gases generated by the reaction of the fuel and the oxidizer. This hot surface, and the mass of hot gases in the chamber, has a pro nounced favorable effect on the self-ignition characteristics of the fuel and oxidizer. Many fuels which are non-hypergolic at the temperature existing in the fuel tank of the rocket unit are rapidly hypergolic in the extremely hot combustion chamber. For economy of operation, a fuel that is hypergolic at very low temperatures may be used to initiate the combustion in and to start the cold reaction motor; the use of this starter fuel may be continued until the hot gases generated have heated the combustion chamber to a high temperature; at this point the flow of the starter fuel can be stopped and a cheaper, although not as highly hypergolic, or even a non-hypergolic fuel, can be utilized for the continuous operation of the reaction motor.

The use of a starter fuel in conjunction with another type of main fuel is particularly advantageous when'very high velocities are necessary. Certain fuels whose decomposition products are of relatively low molecular the very high thrust developed by these fuels. Amen:

to-air missile usually has a relatively short combustion chamber and this fact limits the fuels that can be used for high thrust operation. Turpentine is an excellent high thrust fuel for this use. The turpentine is stored in vessel 26 and valve 28 is closed. About 4 lbs. of RFNA oxidizer are used per pound of turpentine. ethylhexyDphosphine is used as the starter fuel and is Only enough starter fuel to heat up the combustion chamber is needed; in this case 0.1 second of operation. The missile is launched by activating the solenoids in valves 19,, 28 and 33. The turpen-v tine forces the starter fuel into the combustion chamber where the oxidizer and the starter f-uel ignite and heat up the chamber. Without interruption, the turpentine follows into the heated chamber and burns to give the very high thrust reaction.

Thus having described the invention, what is claimed 1s: l. A reaction propulsion method, which method coinp s's injecting ep r ely and s ibs ant v s mult ns ously into the combustion chamber of a rocket motor a nitric acid oxidizer "whichcontains not more than about 10 weight percent of non-acidic materials and a fuel consisting essentially of at least 1 member selected from the class consisting of (a) monoallgylphosphines containing not more than 16 carbon a is, (b) dialkylphQsphines containing not more than 29 carbon atoms and each alkyl substituent containing not more than 16 cal: QQ- .QI S,-% .d (q) T a k ph srih r1 on n n n t more than 9. carbon atoms and each alkyl substituent o t n n o mere. n 6 c r on t m and sa d oxid ze and ai fue r v n e te n a mo a at a rate 'sufiicient to initiate a hypergolic reaction with weight are used for high velcity purposes because of 6 nd to upp rt o bus of the. fu -v 2 he method of claim 1 wherein said oxidizer is white fuming nitric acid.

3 The method of claim 1 wherein said oxidizer is red fuming nitric acid. a

4. The method of claim 1 wherein said oxidizer is nitrogen tetroxide.

5 The. methqd of claim 1 w .i Jr n sa d P osp n is d t t h y )p 0$phi 6. The method of claim lwherein said phosphine is:

triethyl phosphine.

Th thod of a l whe n id Ph9Phi1- mono(dodecy1) phosphinel 7 References Cited in the file of this patent Journal of the American Rocket Society, Ne. 72,

December 1947, page 17. 

1. A REACTION PROPULSION METHOD, WHICH METHOD COMPRISES INJECTING SEPARATELY AND SUBSTANTIALLY SIMULTANE- 